Technical Abstract:
The initial hypotheses behind biochar’s impact on the soil microbial and plant systems have principally been focused on the interaction of the biochar with the soil structure, providing additional microbial habitat, improving water retention and infiltration, improving nutrient availability, buffering or altering the pH of the soil, chemical species sorption, as well as direct fertilization potential of the biochar itself. The focus of this presentation will be on recent laboratory incubations which have shown decreased microbial activity for the biochar + soil system and will illustrate some of the potential mechanisms of these impacts. Recent observations in laboratory soil + biochar incubations have revealed another potential hypothesis to add to the list of effects and that is ethylene production. Ethylene production has been observed from biochar alone (no inoculums) and biochar + soil incubations providing a tantalizing potential factor which could greatly influence both plant and root responses as well as soil microbial responses following biochar additions. The production of ethylene is not constant and not all biochars produce ethylene at equivalent rates. The range of production rates have been observed between 0.5 and 20 ng C2H4/g_soil/ day. Furthermore, ethylene can act as a nitrification inhibitor. This factor partially could explain the decreased nitrous oxide production observed after biochar additions. Nitrification inhibition also could explain the decreased nitrate formation and increased ammonium concentrations observed in soil + biochar incubations. This ethylene stimulation impact does appear to diminish with time from biochar production. However, the temporal trends are still being investigated. The exact cause of this formation is not fully understood. Nevertheless, these observations provide another potential mechanism behind biochar’s impact on both soil and plant systems.